


One Last Try

by Tassledown



Category: Harry Potter - J. K. Rowling
Genre: Black Family-centric (Harry Potter), Creepy fic but not violent, Gen, Implied/referenced abusive family, Regulus lives fic, Retrieving the Horcrux, nonspecific abuse
Language: English
Status: Completed
Published: 2019-08-15
Updated: 2019-08-15
Packaged: 2020-09-01 15:21:41
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 9,543
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20260258
Author URL: https://archiveofourown.org/users/Tassledown/pseuds/Tassledown
Summary: If Regulus reached out and sent Sirius a letter, and Sirius opened it on the day his brother came home from Hogwarts his sixth year before he went to the cave...





	One Last Try

**Author's Note:**

> This is basically self-indulgent Regulus-lives fic that explores how I intend to write magic with the House of Black.

_ ‘Sirius, _

_ I’m sorry. I made a mistake. I don’t know if you’ll read this, but it doesn’t matter. I’ll be dead shortly after the end of the year anyways. I guess I wanted someone to know I realized I was wrong. _

_ I took the mark last year. Mum was proud; Dad hasn’t spoken to me since. He rarely leaves his room anymore. I think he’s given up on all of us for good. I thought Bella might help but she’s busy all the time. Narcissa too. _

_ I miss you. I know we can’t get any of it back, but I do. I miss things when we were kids and we all had each other. I even miss Andy, but most of all I miss you. I think we both knew you were always the one who would survive our family. I just wish it hadn’t taken you from me. _

_ If I never see you again, I at least want you to think better of me than that I was just a fool who did what he was told. I’m not going to die for nothing. If I can’t live like a Black, at least I can die like one. _

_ I love you, still. _

_ Your brother, _

_ Regulus. _

Sirius had been staring at the letter for the last hour. It was the last day of school that year. The school year - Reggie’s sixth year, he wasn’t even _ graduated _ yet - was over. His brother was likely on the train home as he read this.

His little brother had turned seventeen barely two months ago. Sirius had missed his birthday, his adulthood. 

He wondered, inanely, if their parents had even bothered to buy him a watch. Bellatrix had sent Sirius one, for his birthday; he’d packed it away and forgotten it somewhere in his apartment. The Potters had gotten him one too, and he wore that one instead. They were acting more like his family now, but Bellatrix… He remembered the years Regulus had referred to, when their cousins were the only ones in the house who seemed to realize they, the youngest children, had _ existed_.

Unable to stop himself, he got up and dug out the box from the bottom of his dresser. He’d looked at it once, long enough to confirm it was a watch, then shoved it out of sight, unable to think of her without rage or disgust. He couldn’t bring himself to get rid of it but he hadn’t wanted to see it, either.

He put the box on the table, next to Reggie’s letter and opened it. 

The first thing he noticed was that the watch was gold and the band dark red leather. It was classic and elegant - if he put it next to the Potter’s watch, they looked almost identical in style and quality if you didn’t know what you were looking at. The Potter’s watch was black and silver - simple, and inoffensive, a gift from a family that weren’t yet sure of his taste but had wanted to make sure that milestone had not gone unnoticed.

Sirius turned Bellatrix’s gift over in his hands, feeling the quality and the spellwork on it; feeling that it was durable and shatterproof, safe from water and always on time. Feeling the spells she’d added, a jinx repellent, a kind of magic-sight spell on the numbers to see the time at night without light… 

He stopped, with the watch turned on its face and read the engraving on the back of the watch. It was in Gaelic; for privacy, perhaps, or for memory, he wasn’t sure. He wanted to throw the watch out the window the moment he read it: “My lion cub.” 

She’d killed the Bones family the year before he turned seventeen, leaving Amelia Bones to inherit alone. She’d murdered the Assistant Head Auror and his wife and kids the year before… She’d called him that, Christmas his first year, when he came off the train terrified of their family for being a Gryffindor.

Bellatrix had practically _ raised them_, making up for family that didn’t care, and now she’d abandoned him and his little brother. The guilt he felt, for leaving, ate at him: he knew he never should have left him alone. His brother needed him.

It was one thing to run away from his parents. It was another to run away from his _ brother_, his _ responsibility_. His father could strip him of his inheritance, and they might have tried to drive them apart with violence and hatred and favouritism that claimed bias in Reggie’s favour - but he picked up the letter, and he knew it had never worked. 

He shoved Bella’s watch in his pocket and Reggie’s letter after it, and apparated to King’s Cross.

IIII 

His little brother left the train, head down and trunk heavy in his hands. He looked exhausted and when he scanned the platform finally, with both feet set on the concrete he looked hurt to see no one from their family waiting there - until he looked again, and Sirius started walking forward.

Sirius knew why Reggie wasn’t seeing him when he looked. He ran an awkward hand over his short hair and laughed, and Reggie froze, staring at him as he came. 

“Hey Reg,” he said. “It’s been a long time.”

Reggie didn’t move. He looked almost terrified, holding his trunk and staring at him; Sirius smiled crookedly and stopped, just within arm’s reach.

“I got your letter,” he said quietly. “Figured someone should meet you at the station. Do you want to go get a late lunch?”

“I…” Regulus swallowed and handed him his trunk, before he remembered he could do the magic himself. Sirius shrunk it for him anyways and handed it back with a half-smile. Reggie nodded slowly and took it to put into his pocket. “Okay.”

“C’mon.” Sirius led him out of the station and, when Reggie didn’t object, to a muggle cafe up the street he was familiar with. There, he handled the flirting waitress and ordered for them both before he attempted to see if Reggie would be willing to talk. 

“Why are you here?” Regulus asked as the waitress left their tea and walked away. “Truthfully.”

“Because my little brother wrote to tell me he thought he’d done something stupid and was going to die for it.”

“I thought you wouldn’t read the letter.”

Sirius hesitated. “I considered it. But I opened it anyways. I wanted to know. I’m glad I did.”

Regulus picked up his tea cup, blew lightly on the surface then sipped at it - reflexive gestures. Buying time. Sirius looked at him as though he thought he could see something like why, or what was going on, in his face or the curve of his hands. Somewhere in the last decade his little brother had grown up and he hadn’t been watching.

“Are you angry?” Regulus asked suddenly.

Sirius picked up his own tea then. “About what?”

“That I joined up.”

“I’m not angry with _ you_.”

Regulus put down his cup loudly and gave him a disgusted look. “Is everything always about you and Bella still?”

Sirius bristled. “No!”

“Fine, you and your grudge match with Mother, then.”

“_Did _ she make you do it?” Sirius snapped.

“No,” Regulus sighed. “She didn’t _ make _ me do anything. I thought it would make things easier, if I didn’t have to - think, about the future. About everything. You were Father’s _ favourite_, Sirius. Everyone knew I was second-best.”

Sirius laughed, darkly. “Yeah, I was. Daddy’s perfect heir, I remember.”

Regulus sneered. Sirius paused, startled to see it - startled by the vehemence. “I didn’t write to you to complain about this. I’ll deal with it after this, if there _ is _ an after.”

“What is this, then?” Sirius paused and looked up, smilingly, at the waitress as she delivered their food. Regulus startled briefly; he suspected he’d forgotten they were in a restaurant for a time, but relaxed slightly when the food was familiar - Sirius had ordered them both french onion soup and bread, a straightforward meal he knew Reggie had eaten before at home. 

Reggie recovered, once the waitress was gone, and bit his lip, stirring his soup much as he’d fussed with his tea. “Do you remember reading anything about horcruxes, in the library?”

Sirius bit back a reflexive denial, realizing uneasily that had become a habit. He had gotten tired, very quickly, of his friends knowing how much of the Dark Arts he knew. When faced with the Order, he had only begun to deny it more and faster, as he ran into examples more and more often - and whenever he betrayed knowledge, the others watched him with wary eyes.

“It sounds familiar,” he admitted, and tried to recall where it had come up. The library in question had to be the Black library, as Regulus would have been specific if he meant the Hogwarts one. “Something about magical artifacts? It was in one of the histories.”

“We have a book that’s more clear on it, about magical anchorage and soul sight. Horcruxes, it says, is one of the simpler but more damaging ways to achieve temporal immortality.”

Sirius raised both eyebrows. “What the Hell were you looking this up for?”

“I think the Dark Lord made one.”

Sirius felt suddenly very very cold, then flushed, all at once. He leaned forward at the table, and nearly put his elbow in his soup as he forgot it was there - forgot where they were, for a second, in the sheer horror he felt. “_What_, the - how do you know?”

Reggie rubbed at his temples and looked away. “It’s - you know how to see magic. It’s just a second spell for it, more specific, to see souls. I can’t confirm that I know where one _ is_, but I strongly suspect that’s what it was because he’s missing… at least one piece.”

“What _ what _ was?” Sirius started to reach across the table, to touch Reggie’s hand, seeking comfort - for himself or for Reggie, he wasn’t sure, because this was too horrible to contemplate. To his surprise, Reggie reached back and dug in his nails.

He was scared. Of course he was, what had he read so many years ago? It had been a history explaining the madness of a continental Lord: the book had said he’d made a horcrux, and that was of course how he’d lost his mind and forgotten how to be human. He’d been missing half his _ soul _.

It should be no surprise to find out this new Dark Lord had done it, and yet it still felt too horrible to be true. He had to wonder what he’d _ looked _ like, that Reggie wasn’t certain how _ many _pieces he was in.

“He wanted a house elf, last year,” Reggie said, finally. His nails still dug into Sirius’ arm. “I let him take Kreacher, and I told him to go, do what he was told, and come back.” Reggie smiled bitterly at Sirius. “I don’t think Voldemort had wanted him to return.”

“He told you what he’d done?” 

“The short version is, he was setting up a trapped hiding place for an item.” Regulus shrugged, then. “I haven’t tried to go but there’s only so many reasons you’d hide something that thoroughly that isn’t a weapon or… Especially not when it appeared to be Slytherin’s locket. Why would he _ hide _ that, unless it was too valuable to risk?”

Sirius swallowed and nodded, unwilling - and unable - to argue. “You think it really _ is _Slytherin’s locket?” He asked.

“Kreacher saw it, briefly - he knows gold, you know that, and it had the S decal on the outside. Borgin and Burkes registered it as a tested item decades back, so we know it was in circulation again. If this Dark Lord was going to seal his soul in something that _ looked _ like Slytherin’s locket, he’d actually bother to get a hold of the real thing Sirius.”

Sirius laughed. “Okay, you’re right. I can’t argue with that. What were you going to _ do _about it, though?”

“I was going to steal it, and destroy it.”

“What?” Sirius stopped laughing, and brought his other hand up to hold Reggie’s between both of his, as though he could keep him _ there_, and _ safe _ by holding on. “What do you mean, _ steal it_? What…” 

Of course. They were probably the only family in Britain who could idly destroy a horcrux at home: they knew how to cast and control fiendfyre. But…

“What kind of traps did Kreacher have to live through, Reggie?”

Regulus pulled over his napkin and sketched, with finger and magic, as he spoke. “There’s a cave off the coast in Cornwall, it’s hard to get to but not impossible. You’d want to apparate to a rock outside, not in - I was going to have Kreacher take me. You swim inside the cave to an antechamber, pay with blood to open the door, and then you have to cross a lake.

“The boat’s hidden and spelled, but Kreacher couldn’t tell me with what - he doesn’t really see magic the way we do, so it was impossible to get anything that made sense out of him. Something was testing if they were accepted to cross when he got in. It’s also tiny - I think it’s really only meant to hold one person. The boat got them to the island in the middle of the lake and that is going to be the hardest to surpass.” 

Reggie bit his lip and pulled his hands back from the napkin, leaving Sirius to analyze the faintly traced outline as he listened. Sirius offered his hand again and Reggie took it once more, without nails this time. “What’s on the island, then?”

“A podium, with a potion that has to be drunk. He made Kreacher drink it, before he put the locket in. If someone has to drink it to set the trap, someone’s going to have to drink it to pass it.”

“Unless we want to completely break the trap,” Sirius agreed. He looked up and saw Regulus looked disturbed. “What’s wrong?”

“The potion is awful, Sirius,” he admitted. “Kreacher was ill for several days. He couldn’t sleep, had constant waking nightmares. He was constantly thirsty, after that, and the only water in the cave was in the lake which is filled with inferi. When he tried to drink they grabbed him.”

“He’s not a wizard. We could conjure water fine,” Sirius argued.

“So can a house elf,” Regulus snapped. “That’s beside the point, I couldn’t figure out how to help him recover and if we go, one of _ us _ has to drink it.”

Sirius didn’t argue that Regulus had accepted he was coming with him; it was abundantly obvious he couldn’t refuse. “Why can’t we just take Kreacher again?”

Regulus went white and pulled his hand away. Sirius flinched from his retreat, from his face, and looked down. He still had bread that came with his soup. He started ripping it into pieces until his temper had receded enough for him to say, “I’m sorry. I shouldn’t have suggested it.”

“I know he was only ever a _ spy _ to you, Sirius,” Regulus said. His voice still shook with rage. “But he’s not a disposable piece of _ furniture _ either. The only reason we’d take him is to get us to the right place. I was planning to order him to make _ me _drink it when I went.”

“Make him kill you, you mean.” Sirius snapped. “That’s _ much _ better, definitely not going to hurt him at all.”

“Well it’s better than leaving the Dark Lord alive.”

“Did you think _ Mother _ would destroy the locket for you?”

“He knows a lot of magic we don’t, he could destroy it.”

“Reggie, we know thousands upon thousands of spells and there’s still only two things I can think of that could destroy a horcrux: fiendfyre or basilisk venom.”

“_Kharaabi _ Acids would work as well.”

“Let me know when you’ve talked the Turks into trying to ship that to us, then,” Sirius said dryly. “Last I heard nobody’s gotten a container they feel is safe enough to move more than an ounce.”

“An ounce would be sufficient.”

“Kreacher’s still not going to have access to it. You’d have died for nothing. Do you think the potion would be deadly to a human?”

Regulus bit his lip and shook his head. “No, I don’t think it’s deadly in and of itself. I think the inferi are for that. We’re not going to know much more about the protections until we get there.”

Sirius pressed his hands to his eyes and leaned on the table, feeling almost dead with exhaustion at the thought. If Voldemort had a horcrux, and they had a solid guess about where it was, they couldn’t _ not _go. He’d have much preferred to hurt Kreacher but he needed his brother’s cooperation… 

“If we go, and it’s just us, one of us may have to drink it if we’re trying not to rip apart the trap,” Sirius said. He didn’t look up, just waited.

He had several seconds to wait. 

“I likely still should,” Regulus said. “You’ve been fighting for real for a couple years now, you have practice dealing with - if anything unexpected happens. I may have joined but I haven’t actually _ done _ anything yet, I’ve been at school too much. He just wanted Lord Black.”

Sirius swallowed rage, swallowed fury, and swallowed shame before he could talk again. “Alright. What else should we plan for?”

“If we know one of us is going to be incapacitated later on, I’ll pay with blood at the door as well. I’m not sure about the boat…”

“If it’s spelled and appears to be meant for one person, perhaps he only wanted one person to go.” Sirius gestured vaguely and looked up. “You can kind of tell that the protections are meant to be impassable - if the potion _ must _ be drunk to reach the locket and you can’t actually do anything once you drink it, making it so only one person can reach the island would be crippling…”

“What kind of spells would do that, then?” Regulus asked. He started to eat again, finally, and Sirius relaxed a little. “It wouldn’t likely be the obvious, would it? Magical power?”

“Father taught me the spells to cut off someone’s magic, if so,” Sirius admitted. “We’d probably have to leave it on until we got back, though. On top of that, there’s the recovery time after… Any injuries you sustain will take a long time to heal, Reg.”

Regulus brushed that off with a gesture. “But what else? If it’s about - I don’t know, weight, or blood…”

“We’re more related than most brothers, if its blood we could maybe convince it we’re the same person, you’re still pretty slight for your age.”

Regulus nodded, and Sirius also started to eat again. The rest of the meal was spent talking about magical theory as Sirius slowly came to terms with what he’d just agreed to do. 

IIII

Some part of Sirius wanted to plan to take more time, making arrangements and things, but there wasn’t much they _ could _do in terms of planning. Regulus summoned Kreacher and asked him to retrieve the one book Sirius knew he wanted to reference before they went, and… 

That was it. They were going to steal a horcrux. It hadn’t even been a full day since he received Reggie’s letter.

Kreacher took them to the rock on the coastline. Sirius stared up the dark cliff overhead and wondered how on earth Voldemort had even _ found _ this place, seemingly in the middle of nowhere. The cliffs were sheer and, where the water hit, dark and smooth. He couldn’t possibly have known the cave was there from the top, but what he’d been doing at the bottom Sirius didn’t know. 

The waves met the rock with crashes so loud it was hard to believe they would be able to get _ anywhere _in the water, much less into a cave up against the rocks themselves. Reggie was asking Kreacher something, and the elf pointed before vanishing with a crack drowned out by the next crashing wave.

“I wasn’t expecting to be swimming in this,” Sirius shouted, and laughed as he did.

Regulus smiled thinly back at him and without a word startled to climb off the rock into the water, his wand lit and held in his teeth. Sirius followed suit with a curse, bracing himself against the iciness of the water as they swam to a narrow fissure, struggling not to be thrown into the rock before they got inside.

Regulus, in front of him, suddenly acquired the fishbowl-shaped bubble-head charm and dove; Sirius followed reluctantly, but under water was actually less awful than above. They swam into a cave barely three feet wide. Below the surface of the water, the currents sheared less violently side to side. He stayed high, though; lower down he could see fish and other debris being swept back out to sea, and he watched carefully in case Reggie slipped too low.

Finally, the cave ended and rose; he saw Reggie climbing out of the water ahead in the misty light of their wands and followed. There were steps carved into the rock, too even to be anything but magic. Sirius climbed out after him and found Reggie standing, dry, in a large cave above the waterline. 

He blinked, twice, in preparation as he dried his own clothes and let his mind fall into his awareness of the magic around him.

The cave gleamed with it. The steps were carved, yes, and there was a kind of awareness around them although it was the awareness of a large spell fuelled by blood, not an old one that had gained semi-sentience, or an actively watching one.

“Sirius?” Regulus asked. “Is this the door?”

Sirius shook off his sense of the whole spell to focus on just what Reggie meant. The portion of the wall his brother was studying was more complex. It was hard to describe what ‘complex’ meant in these senses; it wasn’t brighter, or substantially different, not really. His father called it a taste when he tried to answer; his cousin usually sensed the desire or will of the spell of some kind.

He wasn’t sure he’d call this intelligence; it certainly didn’t have a taste but it had _ something_, perhaps a texture or a weight on his tongue. While he knew it wanted blood, it wasn’t the same kind of feeling as truly tasting it, or craving it. It felt more like a memory, one that included the gesture in kind.

Reggie caught his arm as he started to move, caught up so deep in his head he hadn’t even thought twice about doing so. “I said I’d do it, remember?”

“Right. Yeah,” Sirius stepped back and let him lead. Reggie pulled a knife from his robes and cut his palm casually. He set it on the rock in the middle of the archway, and it _ was _ an arch, the outline glowing silver as the payment was made. The rock inside the arch vanished to reveal the chamber with the lake.

What Kreacher had told Reggie had been an understatement. 

The cavern with the lake was vaster than Sirius had imagined, or certainly seemed so with the darkness pressing down on them on all sides. A green light shone from the island in the middle, reflected on the completely still water. After the crashing waves outside, the silence and stillness felt ominous.

And the _ magic_.

With his senses open, the cavern felt _ suffocating_. The pressure of the darkness was unnaturally augmented and it laid over him like a blanket on a sweltering summer night. The cave itself had been shaped in large part by magic - perhaps not originally, but it had taken on its current form because of it. The walls were roughhewn stone and they made the smooth lake feel more unnatural by contrast. 

Without a word, he and Regulus both gave the water a wide berth, walking along the shore to find the hidden chain and the boat. Sirius let Reggie look and tried to sort through what he could see, or taste, or feel about the rest of the chamber. 

He concluded that there was an alarm spell on the water, but he’d never seen one like it before. It kept what was in the water quiet, waiting - it would also alert it, or free it, if broken. It was attached to the podium, but without seeing the other piece of the spell there he couldn’t know what for. He didn’t need Kreacher’s report to tell him the ‘it’ in the water was inferi: the spells hung heavy in the air, a memory that this room had known death in such an intimately complex way.

Reggie stopped, in front of him, and Sirius walked into his back and caught himself on his brother’s shoulder. 

“What is it?”

“The chain.” Reggie took hold of thin air, air that felt like biting into a knut or pence piece, and tapped his hand. The copper chain appeared, only just begun to tarnish in the wet air, and dragged itself out of the water onto the bank. 

The boat, when it appeared, was as small as Sirius had feared: Voldemort definitely intended only one person to traverse the lake at a time. The boat itself came to rest against the bank, and Sirius glanced at Reggie and then back to the boat with a sinking feeling.

“It looks like we were right the first time,” Reggie said. “It _ is _ based on magic.”

“I think that’s all Voldemort thinks matters,” Sirius agreed. He tried to study the spellwork more, to see if there was another exception. He crouched to touch the edge of the boat and felt the warding creeping across his skin like Peter’s delicate little rat nails digging in for purchase. He reached out to Reggie and when his brother touched his hand he could feel the spells turn hostile; he jerked his hand back, even though nothing had happened; the boat tried to retreat back underwater until Sirius caught the chain and stopped it. “Right. I’m sorry, Reg.”

“We knew it was a risk. You need to let go of the chain and raise it again.”

Sirius agreed, reluctantly; they’d already violated the spells and had to hope it would reset underwater and come back up. He stood up and let it go, let the boat retreat, and turned anxiously to Reggie. He’d reviewed this spell before they came, knowing it was the simplest way to trick a spell to believe only one person might be there - many wards in the wizarding world discounted the potential of a muggle.

Most wizards would never _ agree _ to this.

Sirius pulled out a stick of charcoal and wrote the runes in question on Regulus’ palms, then dabbed hawthorn oil on his crown, then on his own with a brief few lines of Gaelic.

“For your safety and the safety of the family,” Sirius pulled back and pricked his finger to add his blood to the oil, in case his disownment made the spell fail without proof. “Until such time it is safe for your magic to return.”

The spell took. He felt it, because part of the spell was that it didn’t merely strip magic; magic had to have somewhere to _ go_. What it _ did_, in full, was _ move _ it from one wizard to another: in this case, to family. Sirius closed his eyes and exhaled slowly, trying not to waver in place; normally he'd do this and shunt it into the house wards. Taking it all himself was - dizzying. Reggie’s face had lost all colour. His brother took a shaky breath, then another and leaned on the wall.

“Okay,” he said. “Try again.”

Sirius swallowed and knelt, picking up the chain with a shaking hand. It tested him, but the spell had no memory. It felt what it must assume was a new wizard trying and the boat rose from the water. Sirius held it and reached back for Reggie: the same test as before. This time, when they touched, the wards gave no recognition something was wrong. 

“Now we just have to both fit,” Sirius laughed. 

“Yeah,” Reggie smiled anxiously and stepped up to climb in; Sirius waited for him to be settled, then picked up the chain and followed, sitting tight against his brother’s back. He wrapped an arm around his chest protectively as the boat edged away from the shore. 

The lake warped beneath the boat as it moved unerringly towards the island. The ripples wandered away across the untouched surface, fluttering the alarm spell and masking the dead that rested beneath the surface of the water. The shore and walls of the cavern vanished, and Regulus’ breath against his arm was coming too quickly for his apparent, silent calm. 

Eventually, the boat reached the island. Regulus crawled out first, and Sirius followed him to stand facing the pedestal and its basin at last. 

“What do you see?” Reggie asked.

Sirius winced, realizing Reggie had been rendered blind to everything but the physically obvious details of the cave. He reached out for his hand again and Reggie took it without prompting, clinging to him as they stood facing the pedestal. 

“...The liquid is at least half spellwork, not just a potion,” Sirius answered. “It’s tied to the ward on the water, but I’m not sure exactly what that does. The interactions appear incomplete right now, so I think we have to do something with it before it will become clear.”

“We already had planned to,” Regulus said. “I know you remember how to use fiendfyre, at least; if the inferi wake, we’re safe.”

Assuming Sirius didn’t damage any important spells with it, he thought, but didn’t say that aloud. Regulus needed him to be confident; he had to know what he was doing. He squeezed Reggie’s hand again, then reached out for the liquid, trying to see if anything he could do would interact with it short of the obvious solution. Nothing worked.

He could see, if he had wished, the edges of the spell; he could see where to pull to unravel it, to dissolve the liquid and simply take it. However, doing so would allow the liquid to evaporate completely - a function constrained by the magic, that let it return to the basin once emptied as designed rather than vanish - and if he did so, that part of the trap would have to be completely replaced, not just repaired. 

Neither of them had voiced why they didn’t want to break the trap. If it was obvious they had done something to it, their family would pay the price. Whatever Sirius thought of Bella and Cissy, he didn’t want them dead anymore than he wanted Voldemort to come after him and Reggie. 

Saving Reggie’s life here wouldn’t matter if the Dark Lord wanted them, specifically and personally, dead after this. He had Reggie’s blood on the door, their magic cast in his halls. He knew whose house elf he had used to set the trap. He could find them, if they gave him cause. 

Regulus had not said a word about the time Sirius had taken to study it. When he conjured the goblet, finally, and dipped it into the potion, Regulus tensed and moved closer to him.

“It shouldn’t kill you by itself,” Sirius said. “I promise I’ll get you out, no matter what it does.”

Reggie licked his lips and nodded. “I know you will,” he said. He took the goblet from Sirius and drank. 

Pressed as close together as they were, Sirius felt Reggie’s body tense as he drank; he lowered the cup, empty, and took a long few seconds before he could reach into the basin and refill it, his movements stiff with pain. 

They hadn’t touched, much, since Sirius had started at Hogwarts. The split between them had become vast when he was sorted into Gryffindor, and much of the familiarity that had been present between the cousins had become unacceptable to their mother, then. Where Sirius and Bella, or Bella and her sisters had almost constantly been pressed skin-to-skin for comfort, Reggie had rarely risked reaching out to him since.

Now, as he drank, Regulus leaned more and more heavily into Sirius’ chest, retreating towards that comfort as his limbs began to shake and he refused to open his eyes. 

He managed three drinks before he froze with the cup full and couldn’t finish the gesture. Sirius waited, very still, uncertain what he was seeing or if he should intervene. While the ward’s connection had visibly transferred to him once he drank, the effects of the potion itself were not visible. Sirius didn’t know what was going wrong until Regulus let out a faint whimper.

“Reggie?” Sirius asked.

“It hurts,” he whispered. “I feel sick. I don’t want to…”

Sirius squelched the urge to take the goblet, to stop him, and let his thoughts go cold; to forget to care for the moment because he couldn’t do this if he did. “Reggie, you said you’d finish.”

He had never sounded more like his father in his life; his accent had come back without him thinking about it, and Reggie flinched at the sound. He raised the cup and drank, his throat shuddering around it. He managed another drink after it, on the force of that memory alone and Sirius was gripping his brother’s arm hard enough he knew he’d bruised him.

It wasn’t enough for more than that. Reggie dropped the cup in the potion as he started to dip it again and he flinched back, trying to pull away from Sirius’ arms.

“No, I won’t do it!” he cried. “Let me go, _ please_!”

Sirius dragged him back, then, more terrified he’d fall in the water in his panic than of what the potion had done. Reggie let his legs give out and sank to the base of the pedestal, too weak to stand any longer as he cried.

“It hurts, oh Merlin it hurts… Please, Father, let it stop.”

“Reggie, you have to finish it.” SIrius said. He stood to refill the goblet and crouched again to hold it to his lips. To his relief, the spells had a compulsion: Reggie drank, and swallowed as it came near his mouth, and then he screamed. 

Sirius held him until his scream tapered off to sobs, waiting for him to go limp again, to whimper and give in before he stood and filled the goblet again. Reggie turned his head away and Sirius silently forced him to look back, to take it and drink.

“Please, please, Mother,” Reggie begged. “I didn’t mean to, I wasn’t writing to him, I’m _ not, _ you don’t _ understand… _ No, _ no_, you don’t have to…”

Sirius gave him the drink each time he felt safe letting go, felt sure he wasn’t going to throw himself in the water to end it or by accident; at most he spoke only to order him to drink. Lost in memories and in pain, and trapped by the compulsion, Reggie drank when ordered and thrashed and cried until the immediately worsened effects passed. Sirius simply tried not to think; he focused only on the dropped level of potion, on the slowly revealed locket and the oppressive silence that swallowed the echoes of his brother’s screams.

The last cup filled; the green liquid pooled instantly inside, even as the level had become too shallow to fill it on its own. The locket lay, visible but under a sheen of spell. Sirius shivered, relieved, and gave the last drink to Reggie.

The triumph he felt vanished as his brother drank the last and collapsed in his arms, unconscious. Sirius’ heart hammered in his chest. He checked for a pulse and found it, weak and fast, but present. He stood up and snatched up the locket, shoving it in his pocket and leaving the basin empty behind him. He crouched to pick up his brother and Reggie stirred weakly, mumbling. 

“What is it?” Sirius asked, unable to not respond. 

“Water…” he begged.

Sirius laughed. “Is that all? Didn’t drink enough, did you?” He picked up the cup again and conjured water into its depths. “Here you go, Reg.”

Reggie brought the cup to his lips and the water inside vanished before he could drink.

Sirius’ blood went cold.

He conjured water again and this time held the cup until Reg could try to drink. He saw, then, the flash of magic that had moved onto him and the water in the cup vanished. The wards on the water flashed too, and suddenly he _ knew_.

That was what the wards did. It was a _ curse_.

His brother was panting now, desperate for water and struggling weakly against his arms. Sirius didn’t doubt that he could get him out of the cave and _ still _ he’d be unable to drink another drop. The potion trapped him in nightmares, to paralyze him by the pedestal; the spell, the _ curse_, left him parched for eternity if he didn’t break it.

The other half of the spell was right there, if only he was willing to brave it. 

Sirius lay Reggie down again in the middle of the island and conjured fire, then; ordinary fire, for now, a loop around the perimeter to stop anything coming up except for a gap wide enough for him to reach. He crouched and dipped the cup, as fast as he could.

He wasn’t fast enough. As he came up from the water through the gap he’d left, a murky, white face leapt at him, knocking him down. The goblet fell and spilled across the island; Sirius snarled and shot a jet of flame at the inferius on him. It let go with a shriek and fell backwards, but his concentration had broken: the fire perimeter he’d set had failed. Around them, the other bodies had begun to crawl onto the island, and Sirius gave up on focus and shoved away his wand. 

Fiendfyre leapt up around them as Sirius brought to bear his fury given life and strength. As he’d crushed his care for hurting his brother, he released it, the _ rage _ of what the traps had made him do, and it devoured the wet bodies that had come upon dry land. Those behind the first to die retreated, afraid and confused as their limited awareness was not sufficient for self-preservation against something of that scale. 

When the island had cleared, Sirius got up and crawled to Reggie’s side. He picked up the empty goblet and filled it with water from his wand again, shaking as he tried to hold the fire and the spell in mind at the same time.

This time, the water stayed and Reggie drank; the spell on his skin fluttered loose in tatters as he moved. He emptied the cup and clung to Sirius’ shirt like he never meant to let go.

“It’s okay,” Sirius whispered. “You’re going to be okay.” He’d feared the two parts of the spell would have to touch but either something had connected them or it hadn’t been needed. 

Reggie didn’t speak. Sirius swallowed then, and forced the fiendfyre to go out; he couldn’t risk it near the boat. He recast the ring of fire, a golden loop that felt almost insubstantial after the heaviness of the fiendyre on his skin, but this was not going to be a danger to the spells around them. He picked up Regulus to carry him there. 

It was a struggle to get into the boat when Reggie was too weak to stand, but he managed it regardless. Once he was seated, his brother halfway in his lap, the boat moved and the inferi did not attempt to grasp the sides and pull them under to his immense relief. 

The moment they were on the far side, Sirius got out of the boat, dropped the fire spell and pulled out the hawthorne oil again. He set Reggie against the wall and dabbed it on his wrists, then his head again, fumbling his way through the Gaelic to release his magic once more. He felt what was left of it leave him, but Reggie didn’t immediately respond, just mumbled something under his breath - something that sounded like the standard formula for thanking your Lord - and slipped back unconscious.

Even though he’d expected this, tears stung Sirius’ eyes as he struggled with his frustration. Reggie wouldn’t recover that quickly, even as his magic started to return. Sirius had been burning through his brother's reserves on the island, not his own. He bit his lip until the emotion faded once more. He couldn’t afford it, not yet. 

When he’d mastered his feelings, Sirius picked Reggie up again and carried him out of the cave. The tide still hadn’t retreated enough he felt certain they’d be safe from drowning, and he recast the bubble-head charm for them both before he swam with him out of the cave.

At the rock, he didn’t apparate them back to his apartment; he took him to James and his parents’ home instead. Sirius lay Regulus down on the couch before sending a patronus to Dumbledore, demanding he come. 

He didn’t have to tell anyone else. James’ father, Monty, checked on him within a minute, his face bewildered. “Sirius, what -?”

“Please,” Sirius begged. He’d dropped to his knees on the floor by Reggie’s head. “I don’t know what it did but my brother drank something, he needs help. I already called for Dumbledore for the rest.”

Monty swore and came over; he was better with potions than Sirius, the best option he had short of Madam Pomfrey or the risk of going to St. Mungo’s. Sirius answered his questions about the potion mechanically until James came downstairs, with Lily not far behind. Sirius’ hold on his emotions failed.

“James…” He let go of Reggie finally and staggered to his best friend, crying into his neck. “I don’t know what to do…”

“What happened? Father…”

“I’m not sure,” Monty said. “Sit with him, please. He’s distraught and I need to focus. Can you summon Dumbledore -”

“I did,” Sirius, mumbled. “I need him here, there’s… something I have to give him.”

“He should go to St. Mungo’s,” Monty began, “I’m not sure I’m capable of this…”

“We can’t risk it,” Sirius snapped. “Either Voldemort or our parents will kill him if they find him in this state… Monty, we just stole something the Dark Lord was hiding. That’s why we’re _ here_.”

Sirius felt Monty’s response, more than he saw it; the Potter wards slammed shut and he shuddered a little at the claustrophobic feeling he always had under anti-apparation wards. He fought to shut out his intense sense of magic and the feeling ebbed away as it felt like his senses dulled and the world retreated.

As his senses dulled, his emotions spiked in equal measure. He was sobbing into James’ neck again, before he could get a firmer grip on his feelings, and after this long, he did not try.

IIII

James roused Sirius from his doze on the couch when Dumbledore finally arrived. Sirius sat up, blinking the sleep from his eyes, and trying to remember where he was. He nearly dropped to his knees as Dumbledore came in, too caught up in memories to remember that wasn’t necessary here. He stopped himself from getting off the couch, but he suspected Dumbledore saw something in his face.

“Monty, could we make use of your office for privacy?” Dumbledore asked.

“Yes, of course. I had wanted to ask you about -”

“If you’ll let me talk to him first, I’ll tell him - the details.” Sirius cut off Monty, feeling nowhere near the shame or fear he should have about arguing with someone he’d relied on so long. He needed Dumbledore to know. “He can help more once he’s heard.”

“Alright,” Monty subsided by Regulus’ side again and Sirius went with Dumbledore to his office, feeling much less afraid than when he’d fallen asleep. Even so, Regulus was still out cold. 

Dumbledore sat behind Monty’s desk once inside the room, and Sirius let himself collapse into the seat across from him. He dug into his pocket and pulled out the locket before they began. 

“This is what he got hurt for,” Sirius said. He returned his hand to his pocket, to feel Bella’s watch beneath where the locket had rested. He clenched his hand around it, feeling the dials dig into his palm. “It’s Voldemort’s horcrux.”

Dumbledore sat up straighter and eyed the locket with interest. He studied it for a long minute before he looked up again and sat back. “Can you tell me what happened from the beginning?”

Sirius told him; about the letter, his brother’s evidence and conviction he would die for it, and the cave. He was a curt as possible about the spells he’d used except for the ones that had affected Regulus: about stripping his magic and returning it, and about what he’d seen of the potion and its ward.

Dumbledore listened quietly, staring between him and the locket with quiet interest. “Are you aware of when your brother took the mark?”

“...I assume last year, likely after school.” Sirius clenched the watch tighter; his other arm wrapped around his stomach. “He hasn’t _ done _ anything, Dumbledore, he’s still in _ school_. The Dark Lord just wanted to own Lord Black like all the other houses. He took the mark for the same reason Bella and Cissy did, for the same reason _ I _ considered it as a child.”

“What reason is that?”

Sirius looked up at him and swallowed. “Because he frightened our parents, and he could control them. He could make them back off. I met him - _ Bella _ met him - when he saved her life at my request, in 1968. After that, our parents were too scared to anger her again. It made the house safe.”

Sirius looked down at his hands. “Reggie’s been alone with them since he was thirteen, Dumbledore. He had - nothing, no allies since I ran away and Narcissa was married… Just our stupid house elf. He was my mother’s _ favourite _ and she thought the Dark Lord was a great man who’d bring glory back to our house. She thinks my father is squandering our chances by refusing.

“Sir, please…” Sirius gave in to instinct, to the _ need _ to have him listen to him, and he slid out of his chair and fell to his knees. “Please, you have to let Reggie stay. No one else can protect him, not from Voldemort and our parents. I’ll do whatever you want if you’ll just keep him safe and away from them.”

Dumbledore stood and walked around the desk to his side. Once there, he reached down and, when Sirius took his hands, pulled him back up and into his chair. “There is no need for that, Sirius. I would help you and your brother because you clearly need it. I do not need to be beseeched or pleaded with to provide. Your brother can stay here, or at Hogwarts for the summer; he is still a student, after all, and above his majority.”

“Thank you…” Sirius clung to Dumbledore’s hands, embarrassed but too relieved to let go of his hands. “I didn’t know what to do, but I couldn’t - I couldn’t not help him when I got his letter. I had to; I abandoned him to that - I didn’t think about what they’d do to him if no one else was there.”

He didn’t think about how much they wouldn’t have _ let _ him make a difference anyways; he _ knew _ there had been nothing he could do, and yet still it stung. He bit his lip and let go of his hands to wipe his eyes.

“I… Is he going to be okay?”

“I will need to analyze his condition again to be sure, but your conclusions about the intention of the potion are most likely correct. I do not believe it was ever meant to be fatal in and of itself.”

Sirius nodded slowly, almost giddy with relief. “Please… If you want me to destroy the locket, I could… I can use fiendfyre, we just might want to do it outside.”

“I will let you know when I am prepared to do so, there are some things I can yet learn from the locket while it is intact. First, I should inspect your brother’s condition to be sure… May I take this with me?” 

He picked up the locket, and SIrius nodded furiously; he never wanted to see the thing again. He got up to follow him back out into the living room and sat back down on the loveseat to watch Monty and Dumbledore discuss what had happened to his brother and how to fix it. 

He woke up several hours later on a cot in a guest room. Breakfast was waiting on a tray by his bed, and Reggie was still asleep, kept out cold by a spell. Dumbledore had given Monty some instructions about how to flush the potion out of his system sooner and until they were done Sirius couldn't hold him.

He'd just about hit Monty when he told him that, but had refrained. He knew better; he knew how scared Reggie had been of the aftermath, and if this ended the torment for him, all the better.

It wasn't long before Monty checked on him again; he lifted the spell and left, saying Reggie should wake soon. 

Sirius almost didn't believe him. He was shaking with the memory of holding his brother to make him keep drinking while he begged to be let go. He could almost picture the waking nightmares Reggie must have had from his words, and he felt nauseous even thinking about it.

A noise came from the bed, almost too quiet to hear. Sirius froze, waiting to hear him again, to be sure.

"Sirius?" Reggie whispered.

"I'm here," Sirius got up and went to sit on the bed beside him. He picked up Reggie's hand and his brother squeezed it back. "Hey. We made it. I told you I’d get you out."

"We did?" Reggie asked, his face bewildered. "We got it?"

"Yeah, we got it and we made it back out. It's been about a day, Monty tried to get rid of the potion you drank but I don't know how well it worked."

Reggie closed his eyes and nodded. "The locket…?" 

"Dumbledore has it. He wanted to see what he could learn from it first."

"Make sure he destroys it," Reggie snapped. He opened his eyes again, looking more alert and almost angry. "I don't care what he thinks he can learn."

Sirius laughed and kissed Reggie's hand. "Of course. I promise, I'll check on it again."

"Jerk,” Reggie let him do it and squeezed his hand back. “Am I allowed to get up?”

“I think so. Monty didn’t say you couldn’t. Do you need help?”

“Let me damn well try, Sirius.” 

Sirius backed away and let him, watching anxiously as Reggie got up and crossed the room to the hall and came back a few minutes later. He moved slowly, still visibly weak, but he was reassured to see that he seemed to be okay. Weak was understandable after what had happened. 

“Right,” Reggie leaned back in the bed and squinted at him, his face much clearer after the walk. “Who’s Monty?”

“Mr. Potter, James’ dad. I didn’t think we should risk taking you to St. Mungo’s after that and he’s the best at Potions I know after Madam Pomfrey.”

“No, we can’t risk it.” Reggie covered his face and groaned. “...I don’t even know if I should go back to school.”

“We can talk to Dumbledore about that. Wait and see if he notices what we did.”

“Someone’s going to notice I didn’t go home.”

“Is it that big a surprise, with our family?” Sirius rolled his eyes. “They didn’t even bother to get you a _ watch_, Reggie.”

To his surprise, Regulus flinched and he covered his left wrist with his hand. “They did,” he said. His face was dark, almost angry. “Well, Mother did.”

Sirius searched Reggie’s stricken face and didn’t ask; he wasn’t sure if it was for his brother’s sake or his own. Instead, he took the Potter’s watch off his wrist and offered it to him. “Here,” Sirius said. “You can wear mine.”

Reggie stared at him. “I don’t want you to not have your watch, Sirius.”

“I was given two,” Sirius smiled crookedly. “I might as well start wearing the other one.”

“From who?”

“Monty and his wife gave me that one. Bella sent me another.” He pulled it out then, to let Reggie see it. “Maybe it’ll remind her of what she owes us… I don’t know.”

“...She still says she thinks you might change your mind,” Reggie said, turning the watch over in his hands. He paused at the back, to read the inscription, then shook his head. “You two are absolutely impossible about each other, you know that?” 

Despite the disgust in his tone, Regulus took the black and silver watch and put it on, his hands shaking weakly. They hadn’t been before. Sirius glimpsed the tired look in his eyes and got up, regardless of what Monty had said, and moved to join him on the bed. Regulus moved over to make room and as soon as Sirius was seated, he leaned heavily back against his chest.

“Yeah, I know,” Sirius said belatedly. “I’m sorry she wasn’t there for you.”

He felt Reggie shrug against him. “It’s better this way. She doesn’t have to choose between him or us as long as she doesn’t know.”

“She may never find out, we didn’t really break any of the wards,” Sirius said. “If he doesn’t check on it…”

“He’s going to notice I’m gone. Bella will.”

“Is Bella gonna think you did that or will she assume you vanished for some other reason?”

“...well she might think I’m dead.”

Sirius swallowed at that and stroked Reggie’s hair. “Might not hurt if she does. You don’t have to _ stay _ dead, you’d be safe at Hogwarts if you wanted to go back.”

“I’ll think about it.” Reggie said quietly. “What have you told Dumbledore and the others about me?”

“That you came to me for help, and you’re my little brother, and I love you.” Sirius stroked Reggie’s hair out of his face to smile at him again. “Pretty sure Monty would let you stay too, if you needed. My flat might not be safe enough after what we pulled off.”

“Will James mind? You know he was always picking fights with Slytherins, I don’t want to deal with him being like - like Druella.”

Sirius snorted. “You mean like Pollux. I know you saw him curse everyone just because, Reggie, you don’t have to be polite about it. Nah, he’s calmed down outside school. If he makes trouble for you, I swear I’ll hurt him for it.”

“I don’t want to make your friendships awkward because of me…” Reggie began.

Sirius didn’t answer, then. He could hear, unspoken, the question of what he was doing being friends with someone like James, someone he just casually compared to their grandfather Pollux who _ enjoyed _ voiceless mastery of the Cruciatus, and he didn’t have an answer to that. He pulled Reggie’s hair back again, and felt his brother sigh, quietly; felt him relax against him, and the part of his mind still panicked by fearing he’d hurt him in the cave relaxed too. 

“You won’t,” Sirius said. “How are you feeling, really? I know you said it hit Kreacher harder than this but I don’t know if it was the - the difference in scale or that we got you help or…”

“Probably both,” Regulus said. “I don’t doubt I’ll have nightmares but that’s just because I… remembered things.” He shifted to rub at the watch on his wrist and looked down at it, as though he needed to see and confirm it wasn’t the one he feared it was. 

“Yeah,” Sirius said quietly. “I’m sorry.”

Regulus stared up at him. “What for?”

“...A lot of things. For never noticing how much our family hurt you. Ignoring you, when I shouldn’t have.”

Regulus shrugged, but he stayed silent for several seconds before he replied. “Thank you,” he said quietly. “I know a lot of it wasn’t your fault, but… it could have been easier, if you didn’t agree with them that I was going to be useless.”

Sirius squeezed his brother’s arm and smiled. “You’re definitely not that, I think we proved that last night. You were a better person than I was, then.”

Reggie smiled, then, and he moved lower in the bed, to curl up. Sirius followed and wrapped his arms around his brother’s shoulders. He was facing the door - and anyone who came in - and it felt good to have Reggie curl up against his chest and sleep.

**Author's Note:**

> Kharaabi Acid is something I made up, because it seems silly there's only two ways to destroy them. 
> 
> I write the Blacks as exceptional at certain branches of magic, because there's always a certain focus on the family in the books that implies there's something going on with them beyond the norm.
> 
> This would be effectively a slightly divergence from canon but in the same "universe" as my other Harry Potter fics about Sirius.


End file.
